Composite TiO 2 films modified by CeO 2 and SiO 2 for the photocatalytic removal of water pollutants.

TiO 2 particles of high photocatalytic activity immobilised on various substrates usually suffer from low mechanical stability. This can be overcome by the utilisation of an inorganic binder and/or incorporation in a robust hydrophobic matrix based on rare-earth metal oxides (REOs). Furthermore, intrinsic hydrophobicity of REOs may result in an increased affinity of TiO 2 -REOs composites to non-polar aqueous pollutants. Therefore, in the present work, three methods were used for the fabrication of composite TiO 2 /CeO 2 films for photocatalytic removal of dye Acid Orange 7 and the herbicide monuron, as representing polar and non-polar pollutants, respectively. In the first method, the composition of a paste containing photoactive TiO 2 particles and CeCl 3 or Ce(NO 3 ) 3 as CeO 2 precursors was optimised. This paste was deposited on glass by doctor blading. The second method consisted of the deposition of thin layers of CeO 2 by spray coating over a particulate TiO 2 photocatalyst layer (prepared by drop casting or electrophoresis). Both approaches lead to composite films of similar photoactivity that of the pure TiO 2 layer, nevertheless films made by the first approach revealed better mechanical stability. The third method comprised of modifying a particulate TiO 2 film by an overlayer based on colloidal SiO 2 and tetraethoxysilane serving as binders, TiO 2 particles and cerium oxide precursors at varying concentrations. It was found that such an overlayer significantly improved the mechanical properties of the resulting coating. The use of cerium acetylacetonate as a CeO 2 precursor showed only a small increase in photocatalytic activity. On the other hand, deposition of SiO 2 /TiO 2 dispersions containing CeO 2 nanoparticles resulted in significant improvement in the rate of photocatalytic removal of the herbicide monuron.